How to Design a Permanent Geological Exposure in a Landfill

Bulldozers move trash atop of a 300-feet tall hill at the Simi Valley Landfill and Recycling Center in Simi Valley, California May 8, 2008. Trash, rubbish, whatever you call it, the 1.6 billion tonnes of stuff the world throws away each year -- 250 kilograms per person -- is being touted as a big potential source of clean energy. As concerns about climate change escalate and prices on fossil fuels like oil and natural gas soar to record levels, more companies are investing in ways to use methane gas to power homes and vehicles. To match feature ENVIRONMENT-WASTE/ REUTERS / Hector Mata (UNITED STATES) - RTX5YUZ

One of the most common locations for landfills are worked out quarries and quarries suitable for landfill are an increasingly valuable resource for this reason.

In a growing number of cases suitable sites include rare geological exposures of mineral bearing rock, or strata of regional importance which need to be kept exposed after landfilling for educational and also often for historical reasons.

These SSI’s can result in conflict between conservation and waste disposal interests.

Where quarries used for waste disposal contain Sites of Special Scientific Interest, it is necessary to maintain safe long term access to the geological exposure.

However, it is possible to minimise the conflict and to provide for these geological SSI’s without undue difficulty, as we will describe.

The following list of considerations is broadly based on research described funded by the Nature Conservancy Council in the early 1990s, and has led to the identification of engineering measures designed to optimise landfill void in quarries whilst protecting, in the long term, geological Sites of Special Scientific Interest.

To provide long term, safe, unhindered access to the geological exposure with minimal sterilisation of landfill void space for waste, it is necessary to provide an engineered structure which limits land-take and which maintains a safe and secure perimeter barrier to the waste material.

The presence of a geological exposure in a quarry used as a landfill may have a significant effect on the design and operation of the landfill particularly with respect to leachate management.

Natural drainage should be provided where possible to prevent the accumulation of surface water adjacent to the geological exposure. Where this is not possible or the base of the geological exposure is below the water table, pumping may be necessary to facilitate access to the exposure.

It may be necessary to take measures to prevent the movement of leachate from the landfill site through or beneath the waste retaining structure towards the Site of Special Scientific Interest where it may contaminate accumulating surface and groundwater.

Landfill gas is flammable, is explosive if ignited in an enclosed space, and can also create an asphyxiating atmosphere. In Europe gas hazard sites (such as landfills) are controlled by the ATEX Directive and national regulations, such as the UK’s Dangerous Substances and Explosive Atmospheres Regulations.

Where the landfill perimeter slopes adjacent to the geological exposure are engineered and graded to a profile of less than 1:3 access by visitors on foot across mown ground should present no significant problems if all visitors wear suitable footwear.

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